Field of the Invention
The present invention relates to a feed line formed as a triplate line that runs from a waveguide/triplate-line converter coupled to a radio to a plurality of patch antennas in a cluster pattern.
Description of the Related Art
In satellite communication systems and fixed wireless access (FWA) systems in which wireless transmission is performed in microwave bands and millimeter wave bands over a 10 GHz band, a planar antenna made up of many patch antennas is often employed, and a feed line for these patch antennas is formed as a triplate line in which a structure thereof is simple, parallel feeding can be precisely realized at low cost, and furthermore, gain and efficiency can be highly secured.
As illustrated in FIG. 4, a conventional triplate feed-type planar antenna is made up of, for example, a ground plane 41, a foam sheet 42-1, a flexible substrate 43, a foam sheet 42-2, and a slot plate 44 that are laminated together.
Also, the elements laminated in this way are constituted as follows.
(1) The ground plane 41 is formed with a pattern corresponding to a plane ground on an upper surface thereof.
(2) The foam sheets 42-1 and 42-2 are constituted as cushion material, an insulator, and a dielectric that sandwich the flexible substrate 43 from opposite surfaces thereof.
(3) Along with an array of rectangular patch antennas 43A1,1 to 43Am,n (where m and n are integers) arranged in a lattice pattern, a feed line 43F implementing parallel feeding for these patch antennas is formed at the flexible substrate 43 as a circuit pattern.
(4) Lattice-patterned slot openings 44S1,1 to 44Sm,n are formed in a top surface of the slot plate 44 at regions individually corresponding to the patch antennas, and a plane ground pattern is formed on an overall surface other than these regions.
For example, as illustrated in FIG. 5, a feed system of this triplate feed-type planar antenna is constituted as follows.
A waveguide/triplate-line converter (hereinafter referred to simply as “converter”) 43C is disposed at a predetermined region surrounded by the patch antennas 43A1,1 to 43Am,n on the flexible substrate 43.
Furthermore, a main line 43B is formed on the flexible substrate 43. In the main line 43B, one end thereof continues to a probe 43CP inserted from a sidewall into a pipe of a waveguide 43CWC constituting the converter 43C, the other end thereof continues to a bus bar 43FM of a feed line 43F implementing the aforementioned parallel feeding, and a width thereof is identical to that of the bus bar 43FM.
Also, a transformer 43T, a width of which is set to be narrower than that of the bus bar 43FM, is formed as a circuit pattern in the vicinity of a connection point with the main line 43B on the bus bar 43FM.
As illustrated in FIG. 6, among the constituent elements of the converter 43C, the waveguide 43CWC paired with the aforementioned probe 43CP, as shown in FIG. 5, is made up of the following elements.
(1) A waveguide flange 43CF that corresponds to (is coupled to) one end of a rectangular waveguide connected to a radio (not illustrated) has a rectangular opening continuing into a pipe of the rectangular waveguide, and is disposed in a state in which the opening is in contact with a region corresponding to the ground plane 41.
(2) An annular member 43CR that is formed at the foam sheet 42-1, the flexible substrate 43, and the foam sheet 42-2, which are laminated together, is inserted into a through-hole equivalent to a virtual extension part of the opening, and is formed as a dielectric cylinder having a through-hole through which the aforementioned probe 43CP (FIG. 5) passes.
(3) An annular member 43Cr that is stacked on the annular member 43CR via the slot plate 44 and causes the inside of the pipe of the waveguide flange 43CF to extend to the outside of the slot plate 44 along with the annular member 43CR.
(4) A short circuit plate 43Cs which is installed across a top including an opening of the annular member 43Cr, and in which holes, through which screws 43S-1 to 43S-5 to be described below pass, are formed in the top.
(5) The screws 43S-1 to 43S-5 that are inserted into screw holes formed in the waveguide flange 43CF in correspondence with these holes, and thereby clamp the ground plane 41, the annular member 43CR, the slot plate 44, and the annular member 43Cr between the waveguide flange 43CF and the short circuit plate 43Cs.
The ground plane 41, the annular member 43CR, the slot plate 44, and the annular member 43Cr are previously formed with holes (not illustrated) into which the screws 43S-1 to 43S-5 are inserted and have inner walls of dimensions and shapes to stably come in contact with sidewalls of these screws 43S-1 to 43S-5.
In the triplate feed-type planar antenna having this constitution, the waveguide 43CWC (FIG. 5) is sandwiched between the aforementioned waveguide flange 43CF and the short circuit plate 43Cs by the screws 43S-1 to 43S-5, and is defined by inner walls of the ground plane 41, the annular member 43CR, the slot plate 44, and the annular member 43Cr that are electrically connected by these screws 43S-1 to 43S-5.
Furthermore, in FIG. 5, the probe 43CP converts a transmission wave, which is output by a transmitter (not illustrated) and is forwarded as a basic mode of an electromagnetic field propagated in the pipe of the waveguide 43CWC into an “electromagnetic field of the triplate line.”
On the flexible substrate 43, the “electromagnetic field of the triplate line” is forwarded to the bus bar 43FM via the aforementioned main line 43B and the transformer 43T, and is subjected to the parallel feeding to the patch antennas 43A1,1 to 43Am,n.
In this feeding process, as the width of the transformer 43T is set to be narrower than the width of the bus bar 43FM, the transformer 43T performs impedance matching between the bus bar 43FM and the main line 43B, the widths of which are equally formed.
Therefore, the parallel feeding to the patch antennas 43A1,1 to 43Am,n is inexpensively realized without damage to the triplate line, which makes high gain and efficiency possible.
The prior art related to the present invention includes Patent Literature 1 described below.
Patent Literature 1 discloses a planar antenna that has a constitution of a triplate in which strip lines formed in a board are sandwiched with a space of about 2 mm from opposite sides by ground boards, a radiation element is formed at one of the ground boards, and power is supplied to respective radiation elements by feed lines of the strip lines, and is characterized in that a stripline/waveguide converter is formed in which the strip lines have final feed points whose widths are about 1.7 mm and are inserted from both sides of a waveguide having a size of 19.05 mm×9.525 mm, an interval between the two strip lines is set to about 0.5 to 1.0 mm, and a phase difference between power input into the waveguide from both of the strip lines is set to 180°, thereby making it possible to supply power using a wavelength capable of achieving good power combining (branching) efficiency.